Otitis media, or middle ear infection, is the second most prevalent childhood disease with hearing loss its most common complication. Otitis media also ranks first among the thirty most common diagnoses requiring a physician's office visit up to age 24, accounting for 24.5 million office visits in 1990. Middle ear infections hereby have a tremendous socioeconomic impact worldwide. In the United States alone, costs exceed $3.5 billion/year in medical treatment, surgical management and related loss of income for working parents. Despite the prevalence and significant morbidity associated with otitis media, the pathogenesis of and immune response directed against one of the primary causative agents, nontypeable Haemophilus influenzae (NTHi), is poorly understood and a vaccine is not available. One basis for this lack of understanding is the vast heterogeneity of NTHi which makes defining many parameters of the disease they induce problematic. Until recently, protective antigens had not been identified nd there are still no known antigenic markers. In the last year, however, we have defined the first known virulence factor for NTHi-induced otitis media. Fimbriae, filamentous surface appendages comprised of the subunit protein fimbrin, are adhesins which allow NTHi to colonize the mucosal surface. This adherence confers a selective advantage to this group of microorganisms. Originating from a nasopharyngeal colonization site, fimbriated NTHi more readily gain access to and survive in the middle ear, thus they induce significantly more otitis media than non-fimbriated isogenic mutants. Since fimbriae are pivotal to induction of disease, we hypothesize that immunization with fimbrin protein will result ultimately in the reduced ability of NTHi to colonize the nasopharynx, thus lessening or eradicating its ability to induce otitis media. The specific aims of this proposal are thereby to: 1) employ a new chinchilla model of otitis media which more accurately models human disease to determine if immunization with fimbrin, or conjugated synthetic peptides derived from fimbrin, will induce protection against both homologous and heterologous challenge; 2) use overlapping synthetic peptides to "map" the fimbrin subunit in terms of immunodominant epitopes and eukaryotic cell-binding domains; and 3) to employ several in vitro and in vivo models of adherence and adherence inhibition to better understand this critical host-bacterial cell interrelationship based on pilot data which suggest that adherent NTHi induce changes in the host cell cytoskeleton. All of these aims are designed to examine and define adherence and colonization, the very first event in the pathogenesis of middle ear infection with the goal of being able to inhibit or immunize against this interaction in favor of the host. These studies will further our development of an effective vaccine or intervention strategy against otitis media and will also broaden our understanding of NTHi pathogenesis by providing data on adherence and its inhibition. Only by understanding adherence and all the subsequent pathogenic events which lead to otitis media, can we begin to develop better methods of prevention or treatment.